This invention relates to the treatment of waste liquors containing diazonium salts.
Requirements are increasingly being placed on the chemical industry to dispose of waste liquors in a manner which is considered to be environmentally acceptable. These requirements apply to the dumping of waste on land or at sea, but are particularly severe in their control of the disposal of wastes via the drainage system into inland waterways or coastal waters. Thus, a method of treating waste liquor must at least be able to produce an effluent which may be disposed of by dumping, and preferably also by the more convenient route of discharging into the local drainage system.
Diazonium salts are extensively used in the chemical industry, finding application in the fields of synthesis of aromatic compounds and synthesis of azo dyes, and thus there is a common occurrence of waste liquors containing diazonium salts. Such liquors are generally quite unsuitable for direct release to the environment, whether by dumping or by disposal via the drainage system, firstly because diazonium salts themselves are generally somewhat toxic, and secondly because the liquors are generally aqueous, and most diazonium salts steadily react in aqueous solutions to give, inter alia, a dark colored tar or foam which may be difficult to separate from the liquid part of the liquor.
The tendency of the diazonium salts to decompose to produce a tar or foam may also prevent treatment of the liquor to deal with other environmentally unacceptable components therein. For instance, waste liquors containing diazonium salts often also contain phenolic compounds, and it has been found that attempts to treat the phenolic compounds with an oxidizing agent only increase the evolution of the tar or foam. Attempts to neutralize acidic liquors containing diazonium salts also increase the evolution of the tar and foam.
Thus it is highly desirable to find a method of treating waste liquors containing diazonium salts in order to increase their environmental acceptability, and any such treatment should both reduce the toxicity of the liquor and prevent the diazonium salts therein from decomposing to give a tar or foam.
Very many different reactions of diazonium salts are known in the literature, but on the whole these are unsuitable as methods of treating waste liquors, usually by reason of expense or of the environmental unacceptability of the reagents involved. However, it has now surprisingly been discovered that diazonium salts may be converted into products which do not give rise to tar and foam formation, and which are either less toxic than themselves or may be converted into products that are less toxic than themselves, by reaction with a reagent which is readily available and itself gives rise to no significant problem of waste disposal.